The present invention relates to a ring network system for transmitting multicast information and, more particularly, to a network system wherein a plurality of data processing units (or terminal devices) are connected via node devices (communication control units) to a ring communication channel or transmission line for mutual data communication, and in the case where information of the same content (multicast information) are sent in common from a certain terminal device to other terminal devices, the network system can confirm whether the multicast information has been sent to all of the other terminal devices.
A conventional ring network system, however, is not constructed such that each terminal device generates a response frame signal (hereinafter called merely response frame) upon reception of multicast information. The reason for this is that since a plurality of responses are returned from receiving nodes, collision between responses occurs or the response processing at a transmitting node becomes complicated. Therefore, there arises a problem that it is impossible to confirm whether all of the receiving nodes have received multicast information.